SIMBAD references

We found that multi-periodic low-mass stars discovered by Kepler K2 in the Upper Scorpius association are close binaries with typical separations of the order of 10 au and large mass ratios. These stars were surveyed by speckle interferometry at the SOAR telescope with spatial resolution of 0.''04. Out of 129 observed targets, we resolved 70 pairs (including 16 previously known ones and three new triple systems). The distribution of projected separations of binaries with primary stars less massive than the Sun corresponds to a log-normal with median of 11.6 au and logarithmic dispersion of 0.60 dex, similar to M dwarfs in the field. Future orbits of newly discovered binaries will provide accurate measurements of masses to calibrate pre-main-sequence evolutionary tracks; a tentative orbit of one previously known binary is determined here.